Production of hydroquinone



23, 1955 D. v. ROSS 2,716,138

PRODUCTION OF HYDROQUINONE Filed Aug. 11, 1951 FEED WATER VAPOR TOCONDENSER G-VAC. EQUIPMENT STRIPP/NG COLUM N '1,

CENTR/FUGAL .5 E PA RATOR SULFUR/C A D BAROME TRI C STEAM [REDUCTIONTANK 3 TEAM 16 RECIRCULATING PUMP Donald (Ross INVENTOR.

f MXM ATTORNEYS United States Patent 2,716,138 PRODUCTION OFHYDROQUINONE Donald V. Ross, Kingsport, 'Ienn.,

Kodak Company, Rochester, N. Y., New Jersey assignor to Eastman acorporation of The present invention relates to a process and apparatusfor the production of hydroquinone by meansof reduction of quinone. Moreparticularly, the invention is concerned with an improvement in theprocessand apparatus as disclosed in Von Bramer and Zabriskie U. S.Patents No. 1,880,534 and No. 1,998,177.

The process as disclosed in those patents includes steam distillation ofa quinone-containing mixture to obtain quinone vapor, which is conductedalong with water vapor produced in the distillation to an eductor whereit meets a circulating current of reducing liquid comprising an aqueousslurry of iron dust. The quinone and water vapor, due to a comparativelylow temperature of the circulating liquid reducing slurry and acomparatively high vacuum maintained on the reducing system areinstantly converted or condensed to the liquid phase and the quinone isreduced to hydroquinone. The IIllX- ture of Water and dissolvedhydroquinone passes to a vacuum tank wherein the greater proportion ofthe condensed steam which has entered the system from the steamdistillation step flashes into steam vapor. The vapor is removed by apump and the hydroqumone, being non-volatile, remains behind in theiron-water slurry. The process is continued until all of the quinone hasbeen reduced, the reducing slurry becoming continuously moreconcentrated in hydroquiuone and iron oxide and additional iron dustbeing added from time to time.

While the process as described above has proved quite eflicient, thereare certain operational diificulties which cause considerableinconvenience from time to time. One major problem arises in connectionwith feed of fresh iron dust to the system. The conventional procedurecalls for preparation of a water slurry of fresh iron dust and additionof increments thereof, as required, to the reducing liquid recirculatingin the system, the fresh slurry being introduced by passage thereofthrough a pipe line into the partially evacuated reduction tank. Notonly does the pipe line frequently become plugged under the conditionsof operation but it has proven quite difiicult to obtain a uniformaddition of iron to the system in this manner. Furthermore, therequirement that the iron be added to the system as a slurrynecessitates subsequent evaporation procedures for removal of theadditional slurry water. Another diificulty results because of thecustom of adding iron in large amounts at intervals throughout thereduction process. This custom, while adapted for present commercialinstallations, frequently causes the circulating pump to choke.Additionally, the circulating pump in present practices operates with avacuum at its intake and therefore has a tendency to vapor lock.

In the present systems a large amount of space must be devoted to thereduction tank since it must have suflicient capacity not only to holdthe entire batch, but also to provide sufficient head-room fordisengaging entrained liquid from the flashed vapor. The size of thereduction tank is not only inconvenient because of its Patented Aug. 23,1955 excessive use of space, but also because of the replacementdifiiculties resulting from attrition due to abrasive action of the ironpowder on the inside of the tank walls. Reduction tank maintenancesometimes amounts to a major item in the presently used systems.

It is an object of the present invention to reduce or entirely eliminatethe above mentioned objectionable features which result in practicalinconvenience. Other objects will be apparent from the accompanyingspecification and claims.

The system of the invention includes means for separating, under vacuum,the condensed water vapor from the circulating slurry at a point betweenthe eductor and the reduction tank. The invention also comprises areduction tank maintained at atmospheric pressure and means whereby theseparated hydroquinone and iron dust may be fed by gravity from theevacuated separating means to the reduction tank. Accordingly thereduction tank may be open to the atmosphere whereby dry iron dust maybe fed to it with conventional conveyors, whereby no vapor disengagingaction need be performed therein, whereby little abrasive action uponthe reduction tank walls results from the iron dust, whereby thecirculating pump need not pull against a vacuum, whereby no additionalwater need be introduced into the system in order to add additional irondust, and whereby the reduction tank may be quite small in size relativeto the tanks now in use.

The invention will be understood by reference to the accompanyingdrawing which is a more or less schematic representation of a commercialquinone reduction system.

Referring to the drawing, a quinone steam mixture generated in still pot11 passes upwardly through stripping column 12 and into eductor 13. Thequinonesteam vapor mixture is drawn into a recirculating aqueous slurryof iron dust in the eductor and immediately condensed, the quinonethereupon being reduced to hydroquinone. The aqueous reducing slurry ofiron dust is prepared in reduction tank 14 by the addition thereto asrequired of measured amounts of iron dust from a feeder 15. The slurryis withdrawn from reduction tank 14 by means of recirculating pump 16and continuously passes through recirculation line 17 and the eductor13.

The invention of course is especially concerned with the portion of thesystem between the eductor and the reduction tank. As mentioned above,conventional procedure calls for passage of the slurry containing thecondensed water vapor and the condensed and reduced quinone directlyfrom the eductor to a large reduction tank maintained under vacuum. Inaccordance with the improvement of the present invention, and asillustrated in the drawing, the slurry containing the condensed watervapor and the condensed and reduced quinone passes directly from theeductor 13 to a centrifugal separator (cyclone) 18 which is maintainedunder vacuum. The separator advantageously may be fabricated of castchrome-iron, which is highly resistant to abrasion by the iron slurry.Separation takes place within the centrifuge, water being flashed intovapor therein, withdrawn and passed to a condenser (not shown). From thebottom of the separator 18 extends a barometric leg 19 of suiiicientproportions to maintain a pressure seal. The leg 19 of course projectsbeneath the level of the slurry maintained within reduction tank 14.Sulfuric acid may be added to the system as required through the line20.

In operation, the circulating pump is started and sufficient water addedto the reduction tank to maintain good circulation. The iron dust feederthen is started and its operation controlled either manually orautomatically whereby a uniform feed of iron dust and correctconstripping column.

maintained. The sulfuric acid feed likewise is commenced, and steam isadmitted to the still pot after which feed containing quinone isadmitted to the top of the The centrifugal separator is put intooperation, maintained under a suitable vacuum, e. g. '15" ofimercury andthe reduction process is allowed to operate until all of thequinone-bearing feed has been processed to produce a resultant mixturecontaining hydroquinone; f I V -"The inve'ntionis not limited to singlespecific structural. designs for the centrifugal separator, barometricleg, open-top'reduction tank, and dry iron dust feed conveyor, and itwill be clear to those skilled in the art that various embodiments ofeach of these items may be employed as the occasion demands.

I claim:. a

1'. In a process for the reduction of quinone to producehydroquinonewherein a vapor mixture of quinone and steam is continuously introducedinto a recirculating/reducing slurry of iron dust ,in water, the slurry.being subjected to flashing durin'g'each cycle whereby to removeexcesscondensed steam, the improvement com- .prising the steps of passing theslurrycontainingcondensed steam and condensed and reduced quinone into a'cenfi'ifugal'separator maintained under vacuum, flashing' said slurrywithin said separator whereby to re-, move a portion of'said condensedsteam as water vapor, passingthe unflashed portion of the slurry fromsaid separator through a barometric leg into a reduction tank,maintaining said reduction tank at atmospheric pressure, and introducingiron dust as required into said reduction tankas a dry powder underatmospheric pressure. 2. In a process for the reduction of 'quinone to'pro 'duce hydroquinone wherein a vapor mixture of'quinone,

and steam is continuously introduced into a recirculating reducingslurry of iron dust in water, the slurry being I subjected to'flashingduring each cycle whereby to remove excess condensed steam andincrements ofadditionaliron dust being added to the recirculating slurryfrom time 'to time, the improved method of introducing said additionalincrements comprising passing the re circulating slurry through a zonemaintained at atmos-.

' pheric pressure and feeding said increments into said slurry throughan exposed surface thereof within'said zonc. w

3. Process as defined in claim 2' wherein said increments are added as adry powder.

4.'Process as defined in claim 2 wherein prior to its passage intosaidzone said slurry'is first treated in a condensed steam into saidseparator, an open toppedf reduction tank,'a barometric leg connectingthe sepa rator with said reduction tank and extending to below the levelof liquid in. said reduction tank, and means a for feeding iron dustinto the open top of said reduction tank. i

7. Apparatus for the reduction of quinone to hydro quinone .comprising aline .for'the recirculation of an aqueous reducing slurry of iron dust,an eductor for the introduction of :a vapor mixtureof steam and quinoneinto said line, a centrifugal separator, means for maintaining saidseparator under vacuum, means for introducing eductor efiluent .intosaid separator, an" open? topped reduction tank below said separator, abarometric leg connecting the separator with said reduction tank andextending to belowthe level of liquid .in said re-. duction tank, pumpmeans for withdrawing slurry from said reduction tank and forcing itinto said circulating line and means for feeding dry irondust into theopen top of said reduction tank.

8. An apparatus for reduction of quinone to hydroquinone comprising arecirculating slurry line, means for promoting recirculation of slurrytherein, means for intoducing into said line a vapor mixture of quinoneand steam and means for removing excess condensed steam, an improvedexcess steam removal means comprisinga vacuum centrifugal separator, anopen-topped reduction tank disposed beneath said separator and'abarometricleg providing communication between said separator and saidtank to a point beneath the normal slurry level of the latter.

' References Cited in the file of this patent V UNITED STATES PATENTS1,919,594 Lewis' July 25, 1933' 1,998,177 Von Bramer et al Apr. 16, 19352,107,156

Kuhn et'al, f Feb. 1,

1. IN A PROCESS FOR THE REDUCTION OF QUINONE TO PRODUCE HYDROQUINONEWHEREIN A VAPOR MIXTURE OF QUINONE AND STEAM IS CONTINUOUSLY INTRODUCEDINTO A RECIRCULATING REDUCING SLURRY OF IRON DUST IN WATER, THE SLURRYBEING SUBJECTED TO FLASHING DURING EACH CYCLE WHEREBY TO REMOVE EXCESSCONDENSED STEAM, THE IMPROVEMENT COMPRISING THE STEPS OF PASSING THESLURRY CONTAINING CONDENSED STEAM AND CONDENSED AND REDUCED QUINONE INTOA CENTRIFUGAL SEPARATOR MAINTAINED UNDER VACUUM,FLASHING SAID SLURRYWITHIN SAID SEPARATOR WHEREBY TO REMOVE A PORTION OF SAID CONDENSEDSTEAM AS WATER VAPOR, PASSING THE UNFLASHED PORTION OF THE SLURRY FROMSAID SEPARATOR THROUGH A BAROMETRIC LEG INTO A REDUCTION TANK,MAINTAINING SAID REDUCTION TANK AT ATMOSPHERIC PRESSURE, AND INTRODUCINGIRON DUST AS REQUIRED INTO SAID REDUCTION TANK AS A DRY POWDER UNDERATMOSPHERIC PRESSURE.